Snowmobiles, particularly utility snowmobiles, are sometimes used in areas without groomed trails. In such conditions, it is not uncommon for the front skis of the snowmobile to strike an object hidden from view by the snow, such as a rock or a tree stump. As such, the frames of these snowmobiles must be of a sufficiently rigid construction to withstand these impacts.
Referring to FIG. 1, a prior art snowmobile frame 10 includes a tunnel 12 made of stamped sheet metal having an inverted U-shaped cross section. An endless drive track (not shown) is disposed in part inside the tunnel 12. An engine cradle 14 is rigidly attached to a forward part of the tunnel 12, for example with bolts, by welding, or by forming both together as a single part. The engine cradle 14 supports an internal combustion engine 16 that powers the drive track via a transmission (not shown) to propel the snowmobile. The inherent rigidity of the engine 16 contributes additional rigidity to the engine cradle 14. A front suspension assembly 18 includes a cross member 20 that also forms a forward part of the engine cradle 14. The cross member 20 supports a pair of front skis 22, each via a shock absorber 24. The rigidity of the frame 10 may be further enhanced by the addition of a pyramidal support structure (not shown) connected to the tunnel 12, the engine cradle 14 and the front suspension assembly 18.
In the event that one of the skis of the snowmobile strikes an object, the frame 10 absorbs the forces differently depending on the severity of the impact. Light impacts are absorbed primarily by the shock absorber 24. Heavier impacts are sufficiently strong to fully compress the shock absorber, with the result that the majority of the impact is borne by the rigid portions of the frame 10, namely the tunnel 12, the engine cradle 14 and the front suspension assembly 18. In most cases, the frame 10 is rigid enough to withstand these impacts without sustaining permanent damage. However, it is possible for the impact to be severe enough to cause plastic deformation of the frame 10. The plastic deformation occurs at the portion of the frame 10 that is structurally the weakest, generally either a part of the tunnel 12 or side walls of the engine cradle 14 that form part of the connection between the tunnel 12 and the engine cradle 14. As a result, plastic deformation of the frame 10 generally causes a misalignment between the engine cradle 14 and the tunnel 12, and therefore between components of the transmission that transfer power from the engine 16 to the endless track, potentially rendering the snowmobile inoperable.
Attempting to repair the snowmobile by restoring the shape of the existing frame 10 can result in a less than perfect alignment of transmission components, because the bends cannot always be completely removed. In these cases, it is impossible to adequately repair the vehicle without replacing the entire frame 10, resulting in high repair costs.
Therefore, there is a need for a snowmobile frame having reduced repair costs from sustaining severe impacts.